U.S. Marine Corps Antenna Mcrp 6 22D Operating Instructions

							Chapter 7
Satellite Communications Antennas
The Marine Corps’ primary LOS and SATCOM radio set, the AN/
PSC-5 enhanced manpack UHF terminal, operates at 5 to 25 kHz
and provides data and voice communications. It replaces all man-
packable and vehicular-mounted UHF SATCOM radios. The AN/
PSC-5 provides LOS communications with the AS-3566 and long-
range SATCOM with the AS-3567 and AS-3568 antennas.
Characteristics of the AS-3566 (fig. 7-1) are—
Frequency range (LOS):30 to 400 MHz
Demand assignment
multiple access (DAMA):225 to 400 MHz
Non-DAMA:225 to 400 MHz
Polarization:Directional
Power capability:Determined by terminating resistor
Radiation pattern
Azimuthal (bearing):DirectionalFigure 7-1. AS-3566 Low-Gain Antenna. 
						

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MCRP 6-22D
Characteristics of the AS-3567 (fig. 7-2) are—
Frequency range:225 to 399.995 MHz
Beamwidth:85°
Orientation:Directional
Elevation (0 to 90°)
Input impedance:50 ohms
VSWR:1.5:1
Gain:6 dB (225 to 318 MHz)
5 dB (318 to 399.995 MHz)Figure 7-2. AS-3567 Medium-Gain Antenna. 
						

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Characteristics of the AS-3568 (fig. 7-3) are—
Frequency range:240 to 400 MHz
Beamwidth:77°
Orientation:Directional
Elevation ( 0 to 90°)
Azimuth:  ± 180°
Imput impedance:50 ohms
VSWR:1.5:1 maximum
Gain:8 dB (240 to 318 MHz)
6 dB (318 to 400 MHz)
PowerUp to 150 watts continuousFigure 7-3. AS-3568 High-Gain Antenna. 
						

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MCRP 6-22D
 SITING SATCOM ANTENNAS
The most important consideration in siting LOS SATCOM equip-
ment is the antenna elevation with respect to the path terrain.
Choose sites that exploit natural elevations.
Considerations
The most important consideration in siting over-the-horizon sys-
tems is the antenna horizon angles (screening angles) at the termi-
nals. As the horizon angle increases, the transmission loss
increases, resulting in a weaker received signal.
The effect of the horizon angle on transmission loss is very signifi-
cant. Except where the consideration of one or more other factors
outweighs the effect of horizon angles, the site with the most nega-
tive angle should be first choice. If no sites with negative angles
exist, the site with the smallest positive angle should be the first
choice.
Determining Horizon Angles
The horizon angle can be determined by using a transit at each site
and sighting along the circuit path. Strictly speaking, the on-site
survey will determine the visual horizon angle.  The radio horizon
angle is slightly different from the visual horizon angle; however,
the difference is generally insignificant.
The horizon angle is measured between the tangent at the exact
location of the antenna and a direct LOS to the horizon. The tangent
line is at a right angle (90°) to a plumb line at the antenna site. If the
LOS to the horizon is below the tangent line, the horizon angle is
negative. 
						

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Trees, buildings, hills, or the Earth can block a portion of the UHF
signal, causing an obstruction loss. To avoid signal loss due to
obstruction and shielding, clearance is required between the direct
LOS and the terrain. Path profile plots are used to determine if there
is adequate clearance in LOS systems.
Weak or distorted signals may result if the SATCOM set is operated
near steel bridges, water towers, power lines, or power units.  The
presence of congested air-traffic conditions in the proximity of
microwave equipment can result in significant signal fading, partic-
ularly when a nondiversity mode is employed.
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							Chapter 8
Antenna Farms
The antenna farm (also referred to as the radio hill or the antenna
hill) is a component of a command echelon. It is the location of the
bulk of the unit’s antennas and radio and cryptographic equipment.
It is also the portion of the command echelon that produces the
majority of the electromagnetic radiation. Antenna farms can be
located in several different areas: inside the command echelon, out-
side the command echelon but near it, or outside the command ech-
elon but far from it.
COMMAND POST
The commander exercises command and control through establish-
ing a command post (CP). CPs provide the headquarters facilities
from which the commander and staff operate. Battalions and larger
units may divide the headquarters into three echelons—tactical,
main, and rear. The CP then becomes the echelon at which the com-
mander is physically located.
Tactical
The tactical echelon (main group) is a mobile unit that contains a
minimal personnel and equipment. Its main focus is tactical control
of current operations. The antenna farm will generally be located
within the CP. 
						

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MCRP 6-22D
Main
The main echelon is where the commander is normally located
together with those elements of the staff required to plan and direct
operations and control forces. The antenna farm will generally be
located outside of and far from the CP.
Rear
The rear echelon, located to the rear of the main echelon, focuses on
administrative and logistics functions. It is normally established by
regiments and larger units. It may be located in or near the rear ech-
elon of the senior headquarters or remain aboard ship. The antenna
farm will generally be located outside of and far from the CP.
LOCATION SELECTION CONSIDERATIONS
There are doctrinal, tactical, and technical considerations involved
in deciding of how far the antenna farm should be from the CP. The
CIS officer and CIS chief need to list considerations relevant to the
situation before determining the best location for the antenna farm. 
Doctrinal Considerations
MCWP 6-2 (under development), MAGTF Command and Control,
FMFM 6 (MCWP 3-1 under development), Ground Combat Opera-
tions, and MCWP 6-22, Communications and Information Systems,
contain Marine Corps doctrinal guidance on command echelon
organization and location. 
Some areas to consider when deciding on the antenna farm location
are communications, electronic warfare (EW), tactical situation,
and accessibility. 
						

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Communications
• Take a radio along on reconnaissance to ensure that communi-
cation from the proposed site is possible.
•  Choose another site if communication is not possible.
Electronic Warfare
• Enemy capability.
•  Projected electronic signature of the command. 
Tactical Situation
• Cover and concealment.
• Offense/defense.
• Moving/static.
• Intended length of stay.
• Future operational plans.
•  Speed of displacement.
Accessibility
• Terrain.
• Climate.
•Personnel and equipment available.
Tactical Considerations 
Once the doctrinal issues have been addressed, locating the antenna
farm must be reviewed in the light of tactical considerations. Since
the antenna farm contains the majority of the unit’s radios, crypto-
graphic equipment, antennas, and a fair portion of the radio opera-
tors, the physical safety of the site is an important aspect of the 
						

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MCRP 6-22D
antenna farm location decision. At the division/force service sup-
port group/wing levels, the antenna farm should be remoted 1,000
meters away from the CP, if possible.
Security. The antenna’s physical security depends on the ability to
protect it. The requirement to provide protection depends on the
considerations listed above. Protection considerations also depend,
in part, on the proximity of the antenna farm to the CP. For an
antenna within the CP, no additional protective measures are
required beyond those employed to protect the CP. Additional con-
siderations for the antenna farms located at remote sites follow.
Far Remote Sites
• Security forces available.
• Natural obstacles.
• Perimeter defense, avenues of approach.
• Barbed wire, automatic weapons, deployment.
• Mines and sensors.
•  Supporting coverage.
Near Remote Sites
• Same factors as above apply.
• Take increased EW measures.
• Enforce strict circuit discipline.
•  Use messengers.
Cover and Concealment. Whether the antenna farm is located
inside the unit perimeter or at a remote location, using cover and
concealment is imperative. Security assets make it possible to select
a site that has the best available cover and concealment. Cover and
concealment is a trade-off with the ability to communicate with and 
						

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8-5
from the site. A thoroughly covered and concealed site that prevents
communications is worthless.
Obstacles. As with any other defensive position, use natural or
manmade obstacles to enhance the antenna farm’s security.
Terrain. Studying the terrain in the vicinity of remote antenna farms
is essential to developing an adequate plan for defense. Studying
the terrain is also of paramount importance to ensuring that a unit
can communicate from the site.
Technical Considerations
Siting VHF antennas greatly effects communications reliability. In
an ideal setting, the antenna would be as high as possible above a
flat, clear area. In tactical situations, the antenna location must be a
compromise of propagation consideration, EW considerations, and
cover and concealment. 
When it is possible to see the distant station but not communicate
with it, the receiving station is experiencing destructive multipath
interference. This combining of direct and reflected rays out of
phase, results in complete signal cancellation. This interference can
also result in a very weak signal or one that flutters. To improve
communications, either raise or lower the antenna or move the
antenna to several different sites. Usually, one or both of these
actions will result in good communications.
Another cause of weak communications is antenna cross-polariza-
tion. This means that the transmitting and receiving antennas have a
different polarization. For best communications, both antennas
should be vertically or horizontally polarized.